Bus system with few control lines

ABSTRACT

The invention relates to a bus system, comprising a bus (AIB) for exchanging data (DP) through this bus between two bus interfaces (IAIBC, EAIBC) a first bus control device and a second bus control device for controlling the exchange of data, wherein the first bus control device is allocated to the first bus interface and the second bus control device is allocated to the second bus interface; signaling lines (I-RTR and E-RTR) to signal the respective states of the first or second bus control device; a control line (CTRL) to signal an exchange of data; a data bus (DL) to transmit data (DP) between the two bus interfaces; and a clock line to synchronize the bus system by means of a clock pulse (CL).  
     In order to reduce the number of control lines, it is proposed that the bus control devices be designed to generate a control word (SW) which refers to the data (DP) subsequently to be transmitted, to transmit the control word through the data line or the data bus (DL); and to design these bus control devices to receive the control word, and to relay subsequently received data based on the control information contained in the control word to corresponding connected devices (IF 0  or APX-KERN).

The invention relates to a bus system comprising a bus with the features indicated in the preamble of claim 1, an interface bus formed therewith, and a control method for this bus.

In order to transmit data between two devices, bus systems are conventionally employed with a bus which has bus interfaces to connect the devices transmitting the data. In most bus systems, there is a fixed specification as to which of the connected devices is used as the controlling bus device (master) and which of the devices is used as the serving bus device (slave). Frequent use is also made of a special complex control with so-called memory/DMA-controllers (DMA: direct memory access).

In computers, buses are employed to transmit data between different devices, where control of the data bus is handled by a central processing unit (CPU). For purposes of control, the central processing unit has, in addition to the data bus for data transmission, an address bus to transmit the address of that device of the computer to which or from which data is to be transmitted through the data bus. There are also control lines leading from the central processing unit to the individual devices to signal whether the device in question is to receive data through the data bus or send data through the data bus. In addition, the control lines or control bus serve to determine the instant of transmission through the data bus. The process thus involves a central control of the data transmission through the data bus whereby the central control device enables the data bus for the individual connected devices.

A generally known approach is the principle of handshaking in which the individual devices connected to a data bus communicate with each other, whereby a central processor also organizes coordination of the data access. In addition to the data bus to transmit data between the individual devices, there are at least three lines which are used as control lines. Usually, so-called strobe-acknowledge or interrupt signals are transmitted on these lines. From the point of view of the processor, data input to the processor is effected through the data bus when a connected peripheral device applies the data to be transmitted to the lines and uses a strobe signal to signal the processor that data are available for transmission. The interrupt signal on the interrupt control line serves to signal the peripheral device as to whether an input buffer of the receiving device is empty and that therefore additional data can be applied to the data lines. As soon as the process has initiated the retrieval of data from the input buffer, the interrupt signal is canceled, thereby signaling to the connected peripheral device that another data transmission can be implemented.

In the case of a data output from the device with the processor to the peripheral device, the processor applies the data to the control lines of the data bus and triggers a write pulse. The peripheral device acknowledges retrieval of the data with the acknowledge signal, after which a reset of the interrupt signal notifies the processor that the data bus is ready for a new transmission. In this arrangement as well, assignment of the data bus to transmit data to the individual connected devices is thus performed by the central processor.

Generally known software and hardware interrupts are used to process the interrupts. Hardware interrupts are directed here to interrupt control lines which also enable prioritization of various parallel-received inquiries for data bus arbitration.

Conventional bus systems thus have a data bus, an address bus, and a control bus or corresponding signaling lines and control lines.

Currently available processor chips for digital signal processing, or their central control devices, are usually designed with a large number of random access memory locations (RAM) on the chip or die, with the result that they must be fabricated using the newest possible and expensive method. For many reasons, it is not practical to integrate a multiplicity of interfaces on this type of processor die. However, the highly developed technology needed to fabricate the processor die is not required to provide the interfaces. In light of the variability of requirements related to special interfaces, it is also more practical to provide a separate interface. Additional reasons relate to fabrication parameters and material parameters, for example, dielectric strength. In order to connect a processor core of the control device on a processor die to an interface control device, specifically an interface chip, a bus is required that is fast, requires few lines, has few overheads, and enables different types of transmission; for example, it addresses register and memories individually, or enables direct memory access (DMA).

The goal of the invention is to provide a bus system with a bus which is specifically designed as the interface between a processor core with a conventional bus terminal, and interface devices to additional system devices and peripherals.

This goal is achieved by a system bus having the features of claim 1. Advantageous solutions are also provided by an interface bus for connection between a processor core and interface devices to external devices and equipment, said interface bus having the features of claim 17, or a control method for operating such buses having the features of claim 18.

Advantageous embodiments are presented in the subclaims.

The following discussion explains one embodiment based on the drawings.

FIG. 1 shows a circuit of a bus system;

FIG. 2 is a state diagram of different signals on the lines of a 16-bit bus of this type representing the situation in which an external interface sends a 32-bit data packet.

FIG. 3 is such a state diagram representing the situation in which the external interface sends additional data;

FIG. 4 is a state diagram representing the situation in which the external interface sends data and is then interrupted by the other interface;

FIG. 5 is a state diagram representing the situation in which the external interface requests data;

FIG. 6 is a state diagram representing the situation in which the external interface requests data, while a delay is implemented by the regular bus between the other interface and the processor core;

FIG. 7 is a state diagram representing the situation in which the external interface requests data and is not interrupted;

FIG. 8 is a state diagram representing the situation in which the internal or other bus interface writes data to a region for the external interface;

FIG. 9 is a supplementary state diagram representing the situation in which the internal bus interface reads from an external register region; and

FIG. 10 schematically illustrates one of the bus devices for converting addresses of an address bus between a system bus and the interface bus

FIG. 1 illustrates function elements which help in understanding the bus system described below. A conversion to other bus systems, specifically the use of more or fewer data lines and control lines, is possible using an appropriate rearrangement.

In the embodiment shown, transmission of data is to be implemented between a processor core APX-KERN of a processor device APX to a multiplicity of different interface devices IF0, IF1, IF2, . . . IF15. In a conventional approach, processor core APX-KERN has for this purpose a conventional R-BUS along with data lines, address lines, and control lines.

In addition to processor core APX-KERN, which has, for example, a clock rate of 200 MHz, a bus interface IAIBC is located on the die or chip of processor APX, at which interface the conventional bus R-BUS terminates. Bus interface IAIBC, which for purposes of easier differentiation will hereafter be called the internal bus interface or internal bus control device IAIBC, converts the signals bidirectionally from the conventional bus R-BUS to a bus which hereafter for purposes of easier differentiation will be called the advanced interface bus AIB.

The data to be transmitted from or to another bus interface or bus control device EAIBC are passed through interface bus AIB, said bus control device for purposes of differentiation being called external bus control device or bus interface EAIBC. External bus interface EAIBC serves as the interface between interface bus AIB and additional external interface control devices IF0-IF15 which form interfaces to external devices. This additional bus interface EAIBC and additional external interface control devices IF0-IF15 are in turn located on a chip or circuit board in the form of an external interface arrangement ASD. Conventional devices, such as a computer or external peripheral devices, can be connected in the conventional known manner to additional external interface devices IF0-IF15 in order to communicate with central processor APX and its processor core APX-KERN. The communication here occurs through interconnected interface bus AIB at a rate of, for example, 20 MHz.

In the example shown, this interface bus AIB is composed of n data lines where, for example, n=16, and at least three control lines I-RTR, E-RTR, CTRL. While data and addresses are transmitted through at least one, preferably, multiple parallel data lines, control signals are transmitted through the control lines, the control signals enabling a self-arbitration (self-allocating access) to interface bus AIB. Bus interfaces IAIBC, EAIBC here can have equal access to the bus. A ready-to-read signal IAIBC-RTR from the internal bus control device or bus interface IAIBC, a ready-to-read signal EAIBC-RTR from external bus control device EAIBC, or a control signal CTR are transmitted through the three control lines.

Control signal CTR is used specifically to identify the information or data that is transmitted through interface bus AIB via the data lines as payload (useful data), or as control data or control words SW. In other words, control signal CTR signals whether at a given instant actual payload, or a control word SW announcing or requesting payload, is transmitted through the data lines or data bus DL.

In order to define the access moments in such a way that there is no conflict caused by simultaneous access by the two bus control devices IAIBC, EAIBC to interface bus AIB, bus control devices IAIBC, EAIBC employ the bus clock CL. The different clock pulse edges of clock CL are used here to implement arbitration of interface bus AIB.

In the embodiment shown, internal bus control device IAIBC accesses interface bus AIB whenever a falling clock edge of bus clock CL is present. External bus control device EAIBC is accordingly always allowed to access interface bus AIB whenever a rising clock pulse edge of bus clock CL is present. In an alternative or complementary approach, the state of the bus clock can also be referenced as the criterion, that is, indicating whether the clock signal is in a low or high state.

A simple bus protocol is able to be used as this type of interface bus AIB. For example, the bus protocol can be based on the following fundamental principles.

When the ready-to-read signal IAIBC-RTR from internal bus control device IAIBC is the “high” state, and in this “high” state is transmitted through the corresponding control line I-RTR to external bus control device EAIBC, external bus control device EAIBC is thereby notified that internal bus control device IAIBC is ready to receive a control command. This ready-to-read signal IAIBC-RTR is generated by internal bus control device IAIBC, then applied to the first of control lines I-RTR. In this embodiment, the control signal or ready-to-read signal IAIBC may be modified by internal bus control device IAIBC at any instant during the falling edge of clock pulse CL from interface bus AIB. Alternatively, for example, based on a different bus protocol, it could also be permissible to implement the change in the “low” state of clock pulse CL.

The corresponding ready-to-read signal EAIBC-RTR is generated by external bus control device EAIBC and applied to the second control line E-RTR of interface bus AIB. This ready-to-read signal EAIBC-RTR serves to signal internal bus control device IAIBC that external bus control device EAIBC is ready to receive a control word or data when the ready-to-read signal EAIBC-RTR is in the “high” state. This ready-to-read signal EAIBC-RTR may be modified in the preferred embodiment by external bus control device EAIBC together with the rising edge of clock pulse CL of interface bus AIB. The corresponding alternative is, for example, also permitted whereby changes to this signal are implemented during the “high” state for clock pulse CL.

The control command or control signal CTR can be sent by both bus control devices IAIBC, EAIBC through the corresponding control line CTRL. In the normal state, the control signal is in the “low” state. Whenever one of bus control devices IAIBC, EAIBC wants to transmit control signal CTR, it sets control signal CTR to the “high” state, either briefly or for a longer period of time. In order to prevent a conflict, a determination is also made that in each case only that bus control device IAIBC or EAIBC may activate a control command, for which bus control device the ready-to-read signal IAIBC-RTR or EAIBC-RTR is in the “low” state.

In order to prevent conflicts, the instant of setting control signal CTR to high coincides, for example, with the instant at which corresponding bus control device IAIBC or EAIBC are also permitted to modify the state of their ready-to-read signal IAIBC-RTR or EAIBC-RTR.

In a preferred embodiment, the two bus control devices IAIBC, EAIBC transmit control signal CTR and an assigned control word SW for each rising edge of clock pulse CL. Accordingly, internal bus control device IAIBC is permitted to transmit one control command CTR for each rising edge of clock pulse CL of interface bus AIB. External bus control device EAIBC is permitted to generate a control command CTR together with the rising edge of clock pulse CL of interface bus AIB.

Another advantageous principle of the preferred bus protocol defines that the corresponding ready-to-read signal IAIBC-RTR or EAIBC-RTR remains in the “low” state whenever data or additional data are to be transmitted after control word SW or control command CTR. As a result, the high-setting of the state for ready-to-read signal IAIBC-RTR or EAIBC-RTR of the respective other bus control device EAIBC or IAIBC signals the end of the data transmission.

When interface bus AIB is in the idle state, both ready-to-read signals IAIBC-RTR and EAIBC-RTR are thus in the “high” state, in other words, both bus control devices IAIBC and EAIBC are ready to receive. If one of the two bus control devices IAIBC, EAIBC wants to use interface bus AIB as the controlling device or master, this bus control device IAIBC, EAIBC sets its ready-to-read signal IAIBC-RTR or EAIBC-RTR to the “low” state. In order to avoid arbitration problems, internal bus control device IAIBC changes its state of the ready-to-read signal IAIBC-RTR in response to a rising clock pulse edge of clock pulse CL, while external bus control device EAIBC changes the state of its ready-to-read signal EAIBC-RTR in response to a falling clock pulse edge of clock pulse CL. Bus conflicts are thereby easily avoided. In particular, different bus protocol types may be constructed on this basis. In the following discussion, sample operations based on additional figures are described for different situations.

Preferably, before each newly initiated data transfer, a control command CTR is announced beforehand by a control word SW on data lines DL, and a control command is announced on control line CTRL. Control word SW, specifically, can announce the type of the transfer—for example, to a register, memory, based on DMA (Direct Access Memory)—but also the direction—for example, whether reading or writing is required, and/or the number or address of the addressed external interface device IF0-IF15.

Advantageously, control word SW along with the control line is identified as such. As a result, for example, a read command can be ignored or delayed by bus control device IAIBC, EAIBC receiving this command in order itself to issue a control command of higher priority.

Especially preferred embodiments thus have an interface bus AIB with three or four control lines. In the case of three control lines, these are used to transmit the two ready-to-read signals IAIBC-RTR, EAIBC-RTR, plus the clock pulse CL of interface bus AIB, such that transmittal of control signal CTR is completely eliminated, or is similarly implemented by an appropriately coded control word SW on the data lines. In an embodiment with four control lines, separate control lines are provided in each case for transmission of control signal CTR and of clock pulse CL from interface bus AIB. Clock pulse signal CL thus has the function of a control signal.

The state diagram shown in FIG. 2 provides an example of the case of direct memory access based on DMA by external interface devices IF0 to a memory in the region of central processor APX. Preferably, each of the external interface devices IF0-IF15 has a DMA request line. To initiate a DMA transfer, external interface device IF0 sends a DMA request to external bus control device EAIBC through corresponding direct connection lines or through a regular or conventional bus R-BUS. Transmission of the request through interface bus AIB is then implemented based on the scheme described below.

In the event there is a desired writing to the central memory (DMA-write), that is, external interface device IF0 wants to write data to the central memory, external interface device IF0 sends a DMA request to external bus control device EAIBC. In the case of more than one simultaneous request of this type, the external bus control device decides which of the requests has the highest priority. The other requests are either queued or rejected. External bus control device IAIBC encodes the number or address of external interface control device IF0 and transmits this in a control word SW through interface bus AIB. The transmission here is implemented based on the default requirements described above.

Internal bus control device AIBC scans the received control word SW for the number of external interface device IF0 and checks whether it is a read or write request. If the request is coded in the form of a control word SW or control command as a write request, the system waits until preferably 32 data-bits are available to be transmitted to processor core APX-KERN and to be applied to its input port or R-BUS. Internal bus control device IAIBC then issues a DMA request and passes the data received through interface bus AIB through regular bus R-BUS to processor core APX-KERN, as long as the bus has been so enabled by the processor core.

In FIG. 2, as well as in the following figures showing the state diagrams, the receive or ready-to-read signal IAIBC-RTR is shown in the topmost line. The second line shows the receive or ready-to-read signal EAIBC-RTR from external control device EAIBC. The middle line shows control signal CTR which is transmitted bidirectionally on one of control lines CTRL. Shown below this is the flow of data, specifically data packets with preferably 16-bit data information per data packet, and the flow of control words SW. Shown below this in the last line is the bus clock pulse CL of interface bus AIB which is generated by one of the associated devices or externally, and is then applied to bus control devices AIBC, EAIBC. The illustrated signals IAIBC-RTR, EAIBC-RTR, CTR and CL are, respectively, in the “high” state h or “low” state l, although these states can change sequentially over time as shown moving to the right.

FIG. 2 shows the signal sequence over time when external interface device IF0 sends a data packet to processor core APX-KERN. Initially, the two ready-to-read signals IAIBC-RTR, EAIBC-RTR are in the “high” state. Both bus control devices are thus in the ready-to-receive or ready-to-read state. The control signal is in the “low” state, and no transmission of data takes place. At first time t1, a DMA request is applied at external bus interface EAIBC. At time t1 for the rising edge of clock pulse CL, external bus control device EAIBC changes the state of its ready-to-read signal EAIBC-RTR to “low” (1)-(5). Since the state of ready-to-read signal IAIBC-RTR of internal bus control device IAIBC is in the “high” state, that is, this device is ready to receive, external bus control device EAIBC additionally sends a control signal CTRL by setting its state at time t1 of rising clock pulse edge of clock CL to high. At the same time, an actual control word SW is sent through one of data lines DL from external bus control device EAIBC to internal bus control device IAIBC. Based on the preferred data format, one or more data words or data packets DP follow control word SW, which preferably has a length of 16 bits, the data words or packets each having 16-bit data information (3) at times t2, t3 of the next rising clock pulse edges. As a result, control signal CTR is again set to the low state so that the states or information on data lines DL are recognized by the receiving internal bus control device IAIBC as data, that is, as useful data.

In an optional approach, external bus control device EAIBC can retard or interrupt the transmission if at a later time t4 internal bus control device IAIBC is not in the ready-to-receive state, that is, if ready-to-read signal IAIBC-RTR of internal bus control device IAIBC should happen to be in the “low” state (4), until a new ready-to-receive from internal bus control device IAIBC is signaled by accordingly setting its ready-to-read signal IAIBC-RTR to high at a later time t6 (6).

In the embodiment shown, internal bus control device IAIBC cannot send data directly through regular bus R-BUS to processor core APX-KERN and signals this by the stop signal, that is, by the temporary lowering of ready-to-read signal IAIBC-RTR. In this case, this action has no effect since external bus control device EAIBC has no additional data packets DP to transmit. If the purpose is to provide a priority control, this can be achieved by transmitting appropriate parameters and instructions within control word SW.

FIG. 3 shows the situation in which, for example, first external interface device IF0 sends two data packets and is not thereby delayed or interrupted by a delay on central bus R-BUS to processor core APX-KERN or other transmissions, for example, from or to other external interface devices IF1-IF15. Accordingly, ready-to-read signal IAIBC-RTR from internal bus control device IAIBC is continuously in the “high” state. When applying a transmission request from external interface device IF0 during the next rising-edge change of clock pulse CL to the “high” state, external bus control device EAIBC can accordingly move to ready-to-read, that is, to the ready-to-read signal “low” state (1).

In addition, control signal CTR is set for one clock period to the “high” state to announce the transmission of control word SW (2), (3). At the same time, control word SW is simultaneously placed on data lines DL of interface bus AIB. Since control word SW at the same time contains, or can contain, address information, data lines DL serve simultaneously as address lines.

In the embodiment shown, four data packets DP, each with 16-bit data information, are then transmitted over the next four clock periods of clock CL through one of the data lines to control word SW. The data information of the individual bits, or, as shown, data packets DP can be coded here continually as “high” or “low” base state or, as shown, alternately as “high” and “low.” After the transmission of all supplied data packets DP or data, external bus control device EAIBC again sets its ready-to-read signal EAIBC-RTR at the next rising clock pulse edge of clock pulse CL to the “high” state (4)—it is, in other words, itself again receive-ready for transmissions coming from internal bus control device IAIBC. The transmission stops automatically at the instant no additional data is to be transmitted. As a result, interface bus AIB is simultaneously enabled for new data transmissions and access by one of the two bus control devices IAIBC or EAIBC.

FIG. 4 shows the situation in which external interface device IF0 sends data but is then interrupted by internal bus control device IAIBC. Starting from the state of readiness to read, both for internal and external bus control devices IAIBC, EAIBC, transmission is initiated by external bus control device EAIBC with the rising clock pulse edge in response to the presence of data to be transmitted in this external bus control device EAIBC. To this end, at the rising clock pulse edge of clock pulse CL, ready-to-read signal EAIBC-RTR from external bus control device EAIBC is set to the “low” state (1), a control signal CTR is activated through control line CTRL for one clock period (2)-(3), and a first control word SW is placed on interface bus AIB or its at least one data line. The preferred approach here is an embodiment with an interface bus having 16 data lines DL, so that for each clock period, as shown, one control word SW or one complete data packet DP can be transmitted.

After transmission of control word SW and two data packets DP, external bus control device EAIBC determines that, one half clock period of clock pulse CL earlier, internal bus control device IAIBC has set ready-to-read signal IAIBC-RTR to the “low” state (4), and is therefore not receive-ready. As a result, external bus control device EAIBC can interrupt or delay the transmission of additional data. External bus control device EAIBC moves to the “high” state (5) in order to signal the ready-to-receive state to internal bus control device IAIBC. As a result, at the next rising clock pulse edge of clock pulse CL, internal bus control device IAIBC can in turn activate a control signal CTR for one clock period (6), and simultaneously place a control word SW on data lines DL of interface bus AIB. During subsequent clock pulses, internal bus control device IAIBC places data packets DP on data lines DL. Control word SW and data packets DP are then received by external bus control device EAIBC, evaluated, and supplied to the corresponding external interface devices (7).

One half clock period after sending the last data packet, or at the next falling clock pulse edge of clock pulse CL after sending the last available data packet DP, internal bus control device IAIBC again sets its ready-to-read signal IAIBC-RTR to the “high” state, and is thus again ready to receive (8). Thus, at the next clock pulse edge, external bus control device EAIBC can again move to the send state (9)-(10), as described for the initial transmission of the first control word and first data packets.

FIG. 5 shows the state sequence when, for example, external interface device IF0 requests a DMA read operation. In the example shown, it is assumed that the transmission here is fast and is not delayed or interrupted by processor APX.

Whenever more than one such request is present, external bus interface EAIBC must decide which request has highest priority. All others are queued or rejected. The number or address of external interface device IF0 is coded and transmitted together with the DMA request in a control word SW through interface bus AIB (1)-(2). If this request is decoded as a read request, internal bus control device IAIBC reacts like one of the internal DMA units and sends a DMA request through regular bus R-BUS to processor core APX-KERN. Based on a corresponding allocation, the device applies the 32 data bit to regular bus R-BUS between processor core APX-KERN and internal bus control device IAIBC, then clears the request lines. Internal bus control device IAIBC sends this data through interface bus AIB to external bus control device EAIBC. Here four data packets DP are transmitted, the first 16 data bits of the 32 data bits are first transmitted in a data packet based on the “high” state, then in a second data packet based on the low state, after which accordingly the second 16 data bits are transmitted (5). Once external bus control device EAIBC has finished receiving the 32 data bits, whereby the first data bits may be sent to a buffer, it sends these to the requesting external interface device IF0. Upon buffering the received data, external interface device IF0 clears the request lines and terminates the transmission.

The state diagram in FIG. 5 shows a corresponding sequence. Starting with the ready-to-read state of the two bus control devices IAIBC, EAIBC, external bus control device EAIBC switches to the non-ready-to-read state (1) in response to the arrival of a DMA read request during the next rising clock pulse edge from one of the external interface devices (1). In addition, external bus control device EAIBC places the control signal on control line CTR for one clock period to the “high” state (2). In addition, a corresponding request is generated by external bus control device EAIBC and transmitted through data lines DL to interface bus AIB. Internal bus control device IAIBC receives this control word SW, and switches—ideally after appropriate transmission to processor core APX-KERN—to the non-ready-to-read state only one half clock period later with the next falling clock pulse edge of clock pulse CL (3). After this, external bus control device EAIBC switches back to the ready-to-receive state, preferably already with the next rising clock pulse edge of clock CL, and signals this by setting ready-to-read signal EAIBC-RTR (4) to high. Internal bus control device IAIBC can now apply, with the next clock pulses of clock CL, the data received in the interim through regular bus R-BUS from processor core APX-KERN to data lines DL of interface bus AIB. The external bus control device awaiting data packets receives these data packets DL from interface bus AIB, and relays these to the requesting external interface device IF0 (5).

When the receive memory of external bus control device EAIBC is full, external bus control device EAIBC signals this to internal bus control device IAIBC by setting ready-to-receive signal EAIBC-RTR to low with the next rising clock pulse edge of clock pulse CL (6). Internal bus control device IAIBC then stops transmitting data until there is a new ready-to-receive from external bus control device EAIBC. In this embodiment, internal bus control device IAIBC also closes the line and places itself in the state to receive new commands by setting ready-to-read signal IAIBC-RTR (7) to high. External bus control device EAIBC maintains its ready-to-read signal EAIBC-RTR in this state (8) as long as necessary, at least for one clock cycle of clock CL in the low state, until the memory is once again free, or, as in the embodiment shown, a new DMA request is received through external interface device IF0 or another external interface device IF1-IF15. After this, a control command CTR is once again placed on control line CTRL (9), and a control word SW is applied to data lines DL of interface bus AIB (10).

FIG. 6 describes the situation in which external interface device IF0 requests an individual data transmission which is, however, implemented in a delayed fashion by the conventional bus R-BUS between internal bus control device IAIBC and processor core APX-KERN when processor core APX-KERN is not able to provide the requested data fast enough.

The situation starts based on a ready-to-read state for the two bus control devices IAIBC, EAIBC. After receiving the data request from external interface device IF0, external bus control device EAIBC switches its ready-to-read signal EAIBC-RTR to the non-ready state (1), simultaneously sends a control signal CTR through control line (2), and sends a command or control word SW through data lines DL to internal bus control device IAIBC. As with the previous embodiments, this occurs with the rising edge of clock pulse CL. After one clock cycle, external bus control device EAIBC switches back to the ready-to-read state (3) and waits for a response from internal bus control device IAIBC which has in the interim relayed the request through conventional bus R-BUS to processor core APX-KERN, and which device in turn is awaiting the transmission of data to be passed on. Since the data are initially provided in a delayed manner by processor core APX-KERN, the process of switching internal bus control device IAIBC from the ready-to-read state to the non-ready-to-read state is delayed by one clock cycle relative to the example of FIG. 5 until the data to be transmitted is available. Only then is ready-to-read signal IAIBC-RTR switched to the “low” state (4). As a result of this delay, the internal bus control device continues to remain ready-to-receive so that additional data or requests can be received through interface bus AIB. Blocking of interface bus AIB is thus reduced to the time actually required for the transmission of control word SW and data packets DP. After the data to be transmitted or data packets DP become available, and after switching to the non-ready-to-read state, internal bus control device IAIBC sends the data as data packets DP through data lines DL, where, in the format of the example, one or two 16-bit data packets are transmitted during the next clock cycles.

Optionally, external bus control device EAIBC can retard or interrupt the transmission if its receive memory is full by having ready-to-read signal EAIBC-RTR set to the “low” state (7) for one clock cycle in order to transmit a new control word SW, and issue a control signal or control command CTR through control line CTRL (8). This is possible since after transmitting data packets DP (5) internal bus control device IAIBC has in the interim changed to the ready-to-read state (6). This transmission of an additional control word SW by the external bus control device is thus triggered either by the transition of internal bus control device IAIBC to the ready-to-read state (6) or by the inability of external bus control device EAIBC to receive additional data. Another reason for transmitting an additional control word SW can be the fact that external bus control device EAIBC, for example, must send another, possibly more urgent, DMA request with control word SW through interface bus AIB in the direction of processor core APX-KERN.

After external bus control device EAIBC has transmitted a new, for example, DMA request by issuing the additional control word SW (7, 8), and processor core APX-KERN has accordingly supplied data or data packets DP at internal bus control device IAIBC, the transmission of additional requested data or data packets DP can be implemented directly thereafter without a delay through interface bus AIB to external bus control device EAIBC (9, 10, 11, 12). This operation is implemented as already described for FIG. 5. In this embodiment as well, external bus control device EAIBC again remains immediately ready to read (10) after transmitting the DMA request or corresponding control word SW (7, 8) so as to be able to immediately receive the urgently awaited data DP and relay it to requesting external interface device IF0 (12) after termination of the transmission operation through interface bus AIB (11).

FIG. 7 shows an embodiment for the sequence in the situation when an external interface device IF0 requests data, where a fast transmission is interrupted by processor core APX-KERN. In this example, external bus control device EAIBC sends a first control word SW, in the manner already described, through interface bus AIB to internal bus control device IAIBC. Internal bus control device IAIBC decodes this control word and requests from processor core APX-KERN the data requested by external interface device IF0. After one half clock cycle, internal bus control device IAIBC announces by setting ready-to-read signal IAIBC-RTR to low that the data are available and that it wants to access interface bus AIB (1, 2, 3). External bus control device EAIBC interrupts transmission of additional data or control words and moves after one clock cycle to the ready-to-read state (4).

The external bus control device EAIBC now expects the requested data on data lines DL. However, it has transmitted to it from internal bus control device IAIBC a higher-priority control word SW* through data lines DL (5). Based on the selected data format, data packets (6) follow through data lines DL of interface bus AIB, the data packets belonging directly to the higher-priority control word SW*.

After this data transmission, the internal bus control device again transitions to the ready-to-read state (7). External bus control device EAIBC transmits the received data to an external register or to the appropriate external interface device IF0 indicated within control word SW*, and sends a new request to the bus (8, 9). After this, external bus control device EAIBC sends the original DMA request, which was ignored by internal bus control device IAIBC, once again to interface bus AIB, and then receives the requested data in the manner already described above (8-14).

FIG. 8 shows an example of a state diagram for the situation in which processor APX writes data from its register to an external register. External interfaces IF0-IF15 are controlled by a set of registers which are called external module registers ext IF 0, . . . , ext IF 15, and are interconnected between external bus control device EAIBC and external interface devices IF 0-IF 15. Normally, access to these external module registers is through an internal conventional bus R-BUS. In the interface bus AIB used here which is interconnected between processor APX and external interface device IF 0-IF 15, the corresponding requests of processor APX or of processor core APX-KERN are appropriately translated by internal and external bus control devices IAIBC, EAIBC for transmission through the interconnected interface bus AIB. External bus control device EAIBC implements a retranslation to the conventional format, then transmits the retranslated control signals and data to the requested external module registers ext IF 0-ext IF 15. Transmission through interface bus AIB here can be time-multiplexed if there are problems.

The number or address of each external module register ext IF 0-ext IF 15 to be addressed is coded by internal bus control device IAIBC and transmitted in a control word SW through interface bus AIB, possibly together with information on the data format, to external bus control device EAIBC. This device can implement the retranslation. In order to be able to provide control word SW, internal bus control device IAIBC checks the control signals, address information, and data information received through regular bus R-BUS from processor core APX-KERN in regard to the information to be converted, specifically the register address as well, and in regard to the information as to whether the operation is a read or write operation.

In the case of a write access to external module registers or external interface devices IF0-IF15 by processor APX, the register address is accordingly transmitted by internal bus control device IAIBC to external bus control device EAIBC together with the information that this is a write request. External bus control device EAIBC decodes control word SW received through interface bus AIB and places the corresponding write control signals and addresses of the desired external register on the corresponding bus lines to the external module registers. For the purpose of transmission through interface bus AIB in this case, the transmission of an original word with a 32-bit length is converted to two control words and/or data packets with a 16-bit length, and is appropriately reconstructed by external bus control device EAIBC as a word of 32-bit length, and is only then relayed to external module registers ext IF 0-ext IF 15.

For purposes of illustrating a write operation by processor APX to a selected module register from among external module registers ext IF 0-ext IF 15, FIG. 8 begins from a state with ready-to-read signals IAIBC-RTR, EAIBC-RTR set high, a control signal CTR set low, and a continuous bus clock CL of interface bus AIB. In a first step, internal bus control device IAIBC, after receiving a write request from processor APX, sets its ready-to-read signal IAIBC-RTR to the “low” state, specifically during the next falling edge of clock pulse CL (1). Together with the next rising edge of clock pulse CL, internal control device IAIBC issues a control signal CTR on the control line, and applies a control word SW with the addresses of the desired external module register plus additional information, specifically write information, to data lines DL of interface bus AIB (2). At the start of the next two clock cycles, data packets DP are applied by internal bus control device IAIBC to data lines DL of the interface bus, in each case with the rising clock pulse edges of clock CL (3). After applying the last data packet DP to be transmitted to data lines DL of interface bus AIB, internal bus control device IAIBC sets its ready-to-read signal IAIBC-RTR back to the “high” state (4). It is thus once again ready to read, or ready to receive. In this procedure, external bus control device EAIBC first receives control word SW, whereby external bus control device EAIBC recognizes from the control signal CTR set high over this clock pulse duration (2) that the data on data lines DL of interface bus AIB represent a control word SW. After analyzing the address and type of control command, in this case a write command, external bus control device EAIBC receives data packets DP with the next clock cycles. Since control signal CTR was set back to the “low” state at the end of transmitting control word SW, external bus control device EAIBC recognizes that the information received on data lines DL of interface bus AIB are data which are supposed to be relayed to external interface devices IF0-IF15. Since external bus control device EAIBC has previously received and decoded control word SW, it applies, in parallel with transmission of the received data, the allocated address information and control information to the corresponding control lines so that the relayed data are handled only by the desired external interface device IF0.

Also illustrated is the situation in which external bus control device EAIBC is not able to receive any additional data due to a full receive memory or output memory. In this case, external bus control device EAIBC sets its ready-to-read signal EAIBC-RTR temporarily, here for the duration of one clock cycle, to the “low” state (5, 6). After one or more clock periods, external bus control device EAIBC sets ready-to-read signal EAIBC-RTR back to the “high” state, once it is again able to receive data due to the memory's having been cleared (7). The duration of the “low” state (6) here is a multiple of the clock cycle of clock rate CL for interface bus AIB so as to preclude frequencies higher that clock rate CL of interface bus AIB.

FIG. 9 is a state diagram showing the situation of a read request from processor APX to one of external interface devices IF0-IF15, or to the module register ext IF 0-ext IF 15 allocated to this interface device. Here the corresponding register address, which internal bus control device IAIBC receives through regular R-BUS, is coded, together with additional information, specifically signaling the read request, to a control word SW, then transmitted to external bus control device EAIBC. This device decodes received control word SW and relays this together with the read request to the corresponding external interface device IF0-IF15, or external module register allocated to this device. External interface device IF0-IF15, or its external module registers ext IF 0-ext IF 15, then sends the content of the addressed register to external bus control device EAIBC. This device converts the received data to data packets DP for interface bus AIB, and transmits these through data lines DL to internal bus control device IAIBC. This device implements decoding and relays the data to processor core APX-KERN through regular bus R-BUS as a 32-bit word.

This sequence is seen in the state diagram of FIG. 9. Starting with the states shown in FIG. 8: after receiving a corresponding read request, ready-to-read signal EAIBC-RTR is set by internal bus control device IAIBC to the “low” state together with the next falling clock pulse edge of clock CL of interface bus AIB (1). With the next rising clock pulse edge of clock CL, a control signal CTR is placed on the control signal line, and the generated control word SW is applied to data lines DL of interface bus AIB (2). With the very next rising clock pulse edge, internal bus control device IAIBC moves to the ready-to-read state (3) so as to be able to receive the requested data. With the next rising clock pulse edge of clock CL, that is, after transmitting control word SW, control signal CTR has reset to the “low” state, after which internal bus control device IAIBC waits for the reception of data, or possibly higher-priority control words and data, from external bus control device EAIBC (4). After external bus control device EAIBC has received control word SW and relayed it in decoded form to external interface devices IF0-IF15, the addressed external interface device IF0 applies the data from its external module registers ext IF 0 to the data lines leading to external bus control device EAIBC. This device then receives the data and converts it to a format suitable for interface bus AIB. Subsequently, external bus control device EAIBC sets its ready-to-read signal EAIBC-RTR with the next rising clock pulse edge of clock CL to the “low” state (4), and applies, as long as there are data to be transmitted, corresponding data or data packets to the data lines DL of interface bus AIB over the next clock cycles, each time with the rising clock pulse edge of clock CL (5). After transmitting the last requested data packets DP, external bus control device EAIBC transitions back to the ready-to-read state (6). In parallel with this action, internal bus control device IAIBC receives the data or data packets DP applied to data lines DL of interface bus AIB, and applies these in the appropriate format for regular bus R-BUS to processor core APX-KERN.

Based on this embodiment, it is especially evident that an instantaneous view of the line states do not allow one to clearly determine which state bus control devices IAIBC, EAIBC are in. In state (4) in which external bus control device EAIBC has relayed the read request to corresponding external interface device IF0 and is waiting for transmission of the corresponding data, both the internal and the external bus control device IAIBC, EAIBC seem to be in the inactive wait state. This state has the particular advantage that subsequently either the requested data can be transmitted through interface bus AIB, or it is possible for one of the two bus control devices IAIBC or EAIBC to transmit through interface bus AIB a higher-priority request received in the interim. As the example of FIG. 7 shows, in this case of an interposed control instruction and data transmission the originally requested data transmission would have to be requested once again.

FIG. 10 illustrates a simple embodiment of a bus control device IAIBC or EAIBC. The bus control device can be of very simple design and is essentially composed of multiplexers/demultiplexers MX which adapt the data width of a regular bus R-BUS to the data width of interface bus AIB. In addition, bus control devices IAIBC, EAIBC have a state machine Z, the state of which can be queried by a state register ZR and is settable. As long as the third control line does not also assume a clock function, an external clock CL as the clock of interface bus AIB is applied to control the individual components. State machine Z also selectively either switches incoming address data and state information, or actual data to be transmitted, to data lines DL of interface bus AIB. State machine Z has at least three outputs through which the control information is transmitted to the other communicating bus control device. State register ZR has control lines WR, RE to exchange, specifically, write and read requests with processor core APX-KERN.

One possible advantageous application specifically of this circuit arrangement with this type of bus control devices IAIBC, EAIBC is to connect a microprocessor APX to an interface chip ASD. Use of interface bus AIB and bus control devices IAIBC, EAIBC is particularly advantageous when the goal is to realize a multi-master-capable bus with low controller overhead and few control lines.

Bus control devices IAIBC, EAIBC preferably have a comparator V which compares the priority of previously received read and write requests with the priority of currently received read and write requests, and, based on the comparison, permits or does not permit an interrupt of the current exchange of data. Advantageously, bus control devices IAIBC, EAIBC have a detector (D) which recognizes data congestion on further-extending data lines to external interface devices (IF0-IF15) or to processor core APX-KERN, that is, subsequent receiving devices, and delays the data transmission or data exchange during the time of this data congestion.

It is also possible to link additional bus terminals IAIBC, EAIBC, or to interconnect such bus terminals to other additional bus control devices within the functional range of the bus. In this case, additional signaling lines must be provided to signal the ready-to-read state of the corresponding additionally-introduced bus control device.

The names bus control device IAIBC, EAIBC, and interface bus AIB, serve only to differentiate between the individual components relative to other described components, specifically, relative to conventional buses R-BUS, between which interface bus AIB along with bus control devices IAIBC, EAIBC is interconnected. In general, it is also possible to speak of control devices IAIBC, EAIBC, and one bus AIB. Specifically, the number of data lines DL is also not restricted to the number 16. It is also possible to implement a greater or lesser number of data lines DL. Depending on the ratio of the number of lines for regular bus R-BUS relative to interface bus AIB, a corresponding number of buffers and multiplexers are provided.

Interface bus (AIB) thus advantageously has bus control devices (IAIBC, EAIBC) which are connected between two buses or bus terminals. As is true for conventional buses, the buses or bus terminals each have separate data lines, address lines, and control lines. 

1. Bus system, comprising a bus (AIB) for exchanging data (DP) through this bus between two bus interfaces (IAIBC, EAIBC); a first bus control device (IAIBC) and a second bus control device (EAIBC) to control the exchange of data, wherein the first bus control device (IAIBC) is allocated to the first bus interface, and the second bus control device (EAIBC) is allocated to the second bus interface; a first and a second signaling line (I-RTR and E-RTR) to signal the respective states of the first or second bus control device (IAIBC, EAIBC); a third signaling line as the control line (CTRL) to signal an exchange of data; a data line or a data bus (DL) to transmit data (DP) between the two bus interfaces; and a clock line to synchronize the bus system by a clock (CL); characterized in that the bus control devices (IAIBC, EAIBC) as the transmitting devices are designed to generate a control word (SW) which refers to the data (DP) subsequently to be transmitted, and to transmit the control word (SW) through the data line or data bus (DL); and the bus control devices (IAIBC, EAIBC) as the receiving bus control devices (EAIBC and IAIBC) are designed to receive the control word (SW), and to relay subsequently received data based on the control information contained in the control word (SW) to the corresponding connected devices (IF0, IF1, . . . , IF15, or APX-KERN).
 2. Bus system according to claim 1, in which the bus control devices (IAIBC, EAIBC) are designed to transmit a control signal (CTR) on the control line (CTRL) whenever a control word (SW) is transmitted through the data line or data bus (DL).
 3. Bus system according to claim 1, in which the first and second bus control devices (IAIBC, EAIBC) are designed to code address data, specifically, address data from a conventional bus (R-BUS) and to transmit this as the control word (SW), or to receive this as the control word (SW), and to output it as decoded address data, specifically decoded address data, to a conventional bus (R-BUS).
 4. Bus system according to claim 3, in which the bus control devices (IAIBC, EAIBC) are designed to code control information, specifically, write requests and read requests, to transmit these in the control word (SW) through the interface bus (AIB), to decode these on the receiver side, and to apply these as a control instruction to external devices, specifically, a conventional bus (R-BUS) for as long as data (DP) are subsequently being transmitted through the data line or data bus (DL).
 5. Bus system according to claim 3, in which the bus control device (IAIBC, EAIBC) is designed, after receiving this type of control word (SW), to transcribe previously received control information.
 6. Bus system according to claim 3, in which the first and second bus control devices (IAIBC, EAIBC) are designed to compare the priority of a received request with the priority of an instantaneous transmission through the interface bus in a comparator (V), and to implement an interrupt of the current data transmission for the subsequent transmission of higher-priority data (DP) depending on the comparison result.
 7. Bus system according claim 3, in which the control line is designed to signal (CTR) for bidirectional access by the bus control devices (IAIBC, EAIBC).
 8. Bus system according to claim 3, in which the first and second signaling lines (I-RTR, E-RTR) are of opposite unidirectional design, and are allocated to the first or the second bus control device (IAIBC or EAIBC).
 9. Bus system according to claim 3, in which the first and second signaling lines (I-RTR, E-RTR) are designed to signal the ready-to-receive state or non-ready-to-receive state, and/or a just completed transmission operation of the allocated bus control device (IAIBC or EAIBC).
 10. Bus system, specifically according to claim 3, in which the various bus control devices (IAIBC, EAIBC) are designed to access the bus system only at clearly different clock states of the clock (CL), specifically, with the rising or falling clock pulse edge, so as to prevent conflicts.
 11. Bus system according to claim 10, in which the first and second bus control devices (IAIBC, EAIBC) are designed to access the control line (CTRL) at the instant of the assigned clock state of the clock (CL).
 12. Bus system according to claim 1, in which the bus control devices (IAIBC, EAIBC) each have a comparator (V) to determine and compare the priority of successively received control words (SW) or of control information to be processed, wherein the comparator (V) permits or does not permit an interrupt of the current data exchange depending on the result of comparing the priorities.
 13. Bus system according to claim 1, comprising a detector (D) to determine data congestion on further-extending data lines (R-BUS), wherein the detector (D) delays or interrupts a data transmission through the interface bus (AIB) in the event of such data congestion.
 14. Bus system according to claim 1, in which the first and/or second bus control device (IAIBC, EAIBC) are connected to additional bus terminals.
 15. Bus system according to claim 1, in which the first or second bus control device (IAIBC) is connected to a processor core (APX-KERN), specifically through a conventional bus (R-BUS) to the processor core, and the other, first or second, bus control device (EAIBC) is connected to at least two external interface devices (IF0-IF15), specifically through a conventional bus (R-BUS) to the external interface devices.
 16. Bus system according to claim 15, in which the data transmission rate through the bus, specifically the interface bus AIB), is lower than the data rate through the conventional bus (R-BUS).
 17. Interface bus (AIB) with bus control devices (IAIBC, EAIBC) to be interconnected between two buses or bus terminals, each of which has separate data lines, address lines, and control lines.
 18. Control method for operating a bus system, comprising: a bus (AIB) for exchanging data (DP) through this bus is connected between two bus interfaces (IAIBC, EAIBC); a first bus control device (IAIBC) and a second bus control device (EAIBC) for controlling the exchange of data are allocated to the first bus interface or to the second bus interface; a first and a second signaling line (I-RTR or E-RTR) are used for signaling the respective states of the first or second bus control device (IAIBC, EAIBC) between these devices; a third signaling line is used as a control line (CTRL) for signaling an exchange of data between these lines; a data line or a data bus (DL) is connected and used to transmit data (DP) between the two bus interfaces; and a clock (CL) for synchronizing the bus system is applied to the bus control devices; characterized in that the bus control devices (IAIBC, EAIBC) as the transmitting devices generate a control word (SW) which refers to the data (DP) subsequently to be transmitted; and the control word (SW) is transmitted through the data line or data bus (DL); and the bus control devices (IAIBC, EAIBC) as the receiving bus control devices (EAIBC and IAIBC) receive the control word (SW), decode it, and use it to relay subsequently received data based on the control information contained in the control word (SW) to the corresponding connected devices (IF0, IF1, . . . , IF15, or APX-KERN).
 19. Method according to claim 18, in which the bus control devices as the transmitting devices code an address into a control word (SW), said address being of an additional device (APX-KERN; IF0-IF15) which is connected to a bus (R-BUS) connected to the receiving bus control device. 